Studies conducted under this grant are aimed at characterizing brain circuits underlying pheromone- evoked behaviors and endocrine responses in the mouse. Recent data has demonstrated the involvement of both olfactory and vomeronasal (VNO) systems in pheromone processing and the key role of VNO inputs in ensuring the sex specificity of behavioral responses. These findings raise two fundamental questions: how are olfactory and VNO inputs integrated in order for the animal to achieve physiologically relevant responses, and what is the respective role of each chemosensory system and associated receptors in pheromone processing. We will investigate the hypothesis that specific neuropeptide networks integrate both olfactory and VNO pheromone signals throughout the brain in order to mediate reproduction and aggressive responses. Conditional pseudorabies virus (PRV) and genetic manipulations will be used to trace circuits associated with peptidergic neurons involved in the control of reproduction and aggression, respectively, and to identify specific olfactory and vomeronasal areas and sensory receptors involved. The functional contribution of olfactory and VNO inputs to the uncovered circuits will be further investigated by targeted genetic ablations. These studies will provide critical insights into the mechanisms by which the brain integrates distinct sensory information to regulate the neuroendocrine axis and the expression of appropriate behaviors.